Reduced flow pulsations in a tandem floating cup pump with an odd number of pistons

ABSTRACT

A method for reducing the flow pulsations in a tandem floating cup pump having an odd number of pistons includes determining a low noise net index angle that produces reduced flow pulsations relative to those produced when the net index angle is either zero or half the separation angle and offsetting a first rotating group relative to a second rotating group by the low noise net index angle. The net index angle is the sum of a piston index angle and the port plate index angle. The piston index angle is the angle between a piston from a first rotating group and an adjacent piston from a second rotating group whereas the port plate index angle is the angle by which a first port plate is offset relative to a second port plate.

TECHNICAL FIELD

The present disclosure relates to the field of floating cup pumps and more specifically, to tandem floating cup pumps having an odd number of pistons in each of the two rotating groups.

BACKGROUND

Like all other types of pumps, floating cup pumps generate noise during operation. One source of noise is related to flow pulsations. By reducing the flow pulsations of a floating cup pump, noise related to flow pulsations in the pump may be reduced. It is asserted in the art that flow pulsations in tandem floating cup pumps can be reduced by offsetting one rotating group of pistons with respect to the other rotating group of pistons by a net index angle that is half the separation angle between adjacent pistons. Over the past several years, Dr. Peter Achten has published papers regarding the floating cup pump and improvements related to the floating cup pump concept. In one of his earlier papers, Designing the Impossible Pump, Dr. Achten discusses a twenty-four piston tandem floating cup pump that has an even number of pistons in each rotating group. The paper asserts that the floating cup pump offers higher efficiency, extremely low pulsations and low noise levels. Later, Dr. Achten published another paper titled Reducing Flow Pulsation with the Floating Cup Pump: Theoretical Analysis in which he discusses reducing flow pulsations in the twenty-four piston pump by phase shifting one rotating group of pistons relative to the other by half the separation angle. However, the art has yet to recognize that there might even be a difference between tandem floating cup pumps having an odd number of pistons in each rotating group and tandem floating cup pumps with an even number of pistons in each rotating group. The conventional wisdom appears to suggest that a net index angle of half the separation angle in all tandem floating cup pumps reduces flow pulsations and hence, flow pulsations related noise regardless of the number of pistons in each rotating group. The present disclosure is directed to reducing the flow pulsations and consequently, the noise produced by a tandem floating cup pump having an odd number of pistons in each rotating group.

SUMMARY

In one aspect, a method for reducing flow pulsations in a tandem floating cup pump is described. The floating cup pump includes a first and second rotating group, each having the same odd number of pistons. The pistons being spaced equally apart from adjacent pistons on the same rotating group by a separation angle. The method of reducing flow pulsations includes a step of determining a low noise net index angle that corresponds to reduced flow pulsations in comparison to the flow pulsations produced when the net index angle is zero or half the separation angle. A net index angle between the first rotating group and the second rotating group is set to the low noise net index angle.

In another aspect, a floating cup pump includes a rotor, a first barrel plate and a second barrel plate attached to a shaft. A first rotating group includes a first set of an odd number of floating cups, each being swivelly attached to the first barrel plate. The first rotating group also includes a first set of an odd number of pistons and each piston is equally spaced apart from an adjacent piston by a separation angle. Each piston of the first rotating group has a first end and a second end. The first end of each piston is attached to the rotor and the second end of each piston is received by a respective one of the first set of floating cups. A second rotating group includes a second set of the odd number of floating cups, each being swivelly attached to the second barrel plate. The second rotating group also includes a second set of pistons having the same number of pistons as the first rotating group and each piston is equally spaced apart from an adjacent piston by the separation angle. Each piston of the second rotating group has a first end and a second end. The first end of each piston is attached to the rotor and the second end of each piston is received by a respective one of the second set of floating cups. The first rotating group and the second rotating group have a first relative orientation that defines a piston index angle. A first port plate that is adjacent to the first barrel plate defines a bottom dead center position of the first rotating group. A second port plate adjacent to the second barrel plate defines a bottom dead center position of the second rotating group. The bottom dead center of the first rotating group and the bottom dead center of the second rotating group have a second relative orientation that defines a port plate index angle. A low noise net index angle is the sum of the piston index angle and the port plate index angle and the low noise net index angle is different from the zero and half of the separation angle.

In yet another aspect, a floating cup pump includes a rotor, a first barrel plate and a second barrel plate attached to a shaft. A first rotating group includes a first set of an odd number of floating cups, each being swivelly attached to the first barrel plate. The first rotating group also includes a first set of an odd number of pistons and each piston is equally spaced apart from an adjacent piston by a separation angle. Each piston of the first rotating group has a first end and a second end. The first end of each piston is attached to the rotor and the second end of each piston is received by a respective one of the first set of floating cups. A second rotating group includes a second set of the odd number of floating cups, each being swivelly attached to the second barrel plate. The second rotating group also includes a second set of pistons having the same number of pistons as the first rotating group and each piston is equally spaced apart from an adjacent piston by the separation angle. Each piston of the second rotating group has a first end and a second end. The first end of each piston is attached to the rotor and the second end of each piston is received by a respective one of the second set of floating cups. The first rotating group and the second rotating group have a first relative orientation that defines a piston index angle. A first port plate that is adjacent to the first barrel plate defines a bottom dead center position of the first rotating group. A second port plate adjacent to the second barrel plate defines a bottom dead center position of the second rotating group. The bottom dead center of the first rotating group and the bottom dead center of the second rotating group have a second relative orientation that defines a port plate index angle. A net index angle is the sum of the piston index angle and the port plate index angle. The floating cup pump also includes a means, which includes setting the net index angle to a low noise net index angle that is different from zero and half the separation angle, for reducing noise due to flow pulsations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectioned perspective view of a floating cup pump according to the present disclosure;

FIG. 2 is an enlarged, sectioned perspective view of one floating cup of the floating cup pump of FIG. 1;

FIG. 3 is a perspective view of the rotor of the floating cup pump in FIG. 1;

FIG. 4 is a perspective view of a floating cup pump with a zero net index angle where everything is omitted except one piston from each rotating group and their corresponding floating cups and the ports of the port plates have a zero port plate index angle;

FIG. 5 is a perspective view of the floating cup pump similar to FIG. 4 where the ports of the port plates are offset by a non-zero port plate index angle; and

FIG. 6 is a graphical illustration of the flow rate of a twenty-two piston floating cup pump having a net index angle of zero or half the separation angle and a low noise net index angle for a single rotation.

DETAILED DESCRIPTION

The problem of reducing flow pulsations in a tandem floating cup pump may have appeared to be solved. However, what Dr. Achten and others in the art failed to recognize is the behavioral differences between tandem floating pumps having an odd number of pistons and an even number of pistons in each rotating group. Although the art suggests that offsetting the rotating groups by half the separation angle will provide the best results for reducing flow pulsations, and inherently, the noise related to flow pulsations, the art is wrong when applied to floating cup pumps with an odd number of pistons. The present disclosure teaches one in the art, the best net index angles and associated ranges that provide reduced flow pulsations compared to the levels of flow pulsations when the net index angle is zero or half the separation angle.

Referring to FIGS. 1 and 2, a twenty-two piston tandem floating cup pump 10 is shown. Although the disclosure is applicable to tandem floating cup pumps having any odd number of pistons in each rotating group, the twenty-two piston tandem floating cup pump is described as an exemplary embodiment of the disclosure. The pump 10 includes a shaft 18, a rotor 12, a first rotating group 20, a second rotating group 50, a first port plate 40 and a second port plate 70. The first rotating group 20 includes eleven pistons 22, eleven floating cups 31 and a first barrel plate 26. The second rotating group 50 also includes another eleven pistons 23, eleven floating cups 31 and a second barrel plate 56. Both the rotating groups contain the same number of pistons and an equal number of floating cups as the number of pistons. Each piston 23 has a rotor end 24 that is attached to a first side 15 of the rotor 12. Each piston 23 also has a cup end 25 that is received by a corresponding floating cup 31. In the first rotating group 20, a bottom end 34 of each floating cup 31 is swivelly attached to a cup side 27 of the first barrel plate 26. The term swivelly attached means the floating cups can swivel about the point of attachment while they are attached to the barrel plate. The first barrel plate 26 rotates on an inner side 41 of the first port plate 40. In the second rotating group, the bottom end 34 of each floating cup 31 is attached to the cup side 57 of the second barrel plate 56. The second barrel plate 56 rotates on an inner side 71 of the second port plate 70.

In the tandem floating cup pump 10, the two rotating groups 20 and 50 are structurally and functionally similar and therefore describing the first rotating group 20 shall suffice to understand the structure of the second rotating group 50. The floating cup 31 has an inner cylindrical wall 32, which is in contact with the cup end 25 of the piston 23. A bottom end 34 of the floating cup 31 has a hole 33, which allows a fluid to flow in and out of the first barrel plate 26 through the port plate 40 from an inlet port 48 and to an outlet port 49 (not shown in FIG. 2, see 149 in FIGS. 4 and 249 in FIG. 5). The rotor end 24 of the piston 23 may be narrower than the cup end 25 of the piston 23 to prevent the piston 23 from slipping out of the floating cup 31 and also providing the floating cup 31 with more room to swivel.

Referring in addition to FIG. 3, the rotor 12 of the floating cup pump 10 in FIG. 1 is shown. The rotor 12 includes a first side 15, a second side 16, a bore 13 that receives the shaft 18 and twenty-two holes 14 that pass through both the first side 15 and second side 16 of the rotor 12. In other embodiments, the holes 14 may not pass through the entire thickness of the rotor 12. Each alternate hole 14 receives a piston 23 from the first rotating group 20 while the remaining holes 14 receive pistons 23 from the second rotating group 50. Hence, adjacent pistons 23 from the first rotating group 20 are spaced apart by the separation angle 29 and adjacent pistons 23 from the second rotating group 50 are also spaced apart by the separation angle 29. The angle between a hole 14 that receives a piston 23 from the first rotating group 20 and a hole 14 that receives a piston 23 from the second rotating group 50 defines a piston index angle 90. Because the pistons 23 of each rotating group 20 and 50 are attached to the holes 14, the piston index angle 90 is also defined by the relative orientation between the first rotating group 20 and the second rotating group 50. The piston index angle 90 can be a positive or negative angle based on the Right Hand Rule. A piston index angle 90 greater than half the separation angle 29 is equivalent to a negative piston index angle whose magnitude is equal to the difference between separation angle 23 and the piston index angle 90. Consequently, the maximum piston index angle possible is half the separation angle 29.

Referring to FIG. 4, a floating cup pump 110 with everything omitted except one pair of pistons 123 and its corresponding pair of floating cups 131 is shown. One of the two pistons 123 and its corresponding floating cup 131 are from the first rotating group 120 while the other piston 123 and its corresponding floating cup 131 is from the second rotating group 150. The pistons 123 are aligned together, therefore the pump 110 has a piston index angle of zero. In a pump with a zero piston index angle, the rotor would have eleven holes, each of which is shared by one piston from the first rotating group and one piston from the second rotating group. The rotating groups 120 and 150 rotate on the port plates as the pistons 123 rotate between the bottom dead center and the top dead center of their respective rotating groups. Each rotating group has a bottom dead center and a top dead center orientation. The bottom dead center of a piston in a rotating group is where the pistons define a maximum fluid volume in the pumping while the top dead center of a rotating group is where the pistons define a minimum fluid volume in the pumping chamber. The first port plate includes an inlet port 148, and outlet port 149, a bottom blocked portion 144 and a top blocked portion 145. The second port plate includes an inlet port 178, and outlet port 179, a bottom blocked portion 174 and a top blocked portion 175. In the floating cup pump 110, the bottom blocked portions 144 and 174 of the first and second port plates are aligned in the same plane which means the angle defined as a port plate index angle is zero. The sum of the pump's piston index angle and port plate index angle is the net index angle. The maximum magnitude for the net index angle is the separation angle of the pistons. In the pump 110, the net index angle is zero, which means the first rotating group 120 and the second rotating group 150 are in phase. When the net index angle is zero, a piston 123 from the first rotating group 120 displaces the same amount of fluid as a corresponding piston 123 from the second rotating group 150 at the same time.

Referring to FIG. 5. A similar floating cup pump 210 to the one in FIG. 4 is shown. The piston index angle is zero as both pistons 223 from the rotating group 220 and 250 are aligned. The first port plate includes an inlet port 248, and outlet port 249, a bottom blocked portion 244 and a top blocked portion 245. The second port plate includes an inlet port 278, and outlet port 279, a bottom blocked portion 274 and a top blocked portion 275. However, the port plates have been offset relative to each other by a port plate index angle 292. By offsetting the port plates relative to each other, the bottom dead center of the first rotating group 220 passes a specific point on the bottom blocked portion 244 of the first port plate at a different moment than when the bottom dead center of the second rotating group 250 passes a corresponding specific point on the bottom blocked portion 274 of the second port plate. The offset allows the first rotating group 220 to function at a slightly different phase than the second rotating group 250. The port plate index angle 292 can be a positive or negative angle based on the Right Hand Rule. The maximum port plate index angle is half the separation angle. A port plate index angle greater than half the separation angle is equivalent to a negative port plate index angle whose magnitude is equal to the difference between the separation angle and the port plate index angle.

Referring to FIG. 6, which shows a graphical illustration of fluid flow rate for one rotation of the pump 10 normalized to pump speed, plot 83 represents the flow rate over one period of rotation when the two rotating groups 20 and 50 have a zero net index angle. Plot 84 represents the flow rate over one period of rotation when the two rotating groups 20 and 50 have a net index angle 90 of half the separation angle. It may be appreciated that the plots 83 and 84 appear to overlap each other. The plot 87 represents the flow rate over one period of rotation when the two rotating groups 20 and 50 are offset by a net index angle set to a low noise net index angle. A low noise net index angle is a net index angle for which the noise related to flow pulsations is lower than the noise related to the flow pulsations produced at a net index angle is zero or half the separation angle. It is known in the art that the swing from the average flow rate determines the magnitude of flow pulsations. The larger the magnitude of the swing, the larger the flow pulsations and consequently, the greater the noise related to flow pulsations. From the plots, it is obvious that the swing of plot 87 is much smaller than the swing of plots 83 and 84. Therefore, the flow pulsations and the noise related to flow pulsations produced by a pump with a net index angle set to the low noise net index angle will be substantially smaller than that produced by a pump having a net index angle of zero or half the separation angle. Although not shown, floating cup pumps may exhibit maximum flow pulsations at a high noise net index angle that is also different from zero and half the separation angle.

In an exemplary embodiment, a floating cup pump may have a non-zero piston index angle and a zero port plate index angle or a zero piston index angle and a non-zero port plate index angle. In another embodiment, a pump may have a non-zero piston index angle and a non-zero port plate index angle. A low noise net index angle is a net index angle where the noise produced by the floating cup pump is lower than the flow pulsation related noise produced by the floating cup pump when the net index angle is set to either zero or half the separation angle. A best low noise net index angle is a net index angle where the noise related to flow pulsations is at a minimum level for that given pump. Because noise related to flow pulsations is a function of the number of pistons in the pump and the net index angle of the pump, setting the same net index angles in pumps having different number of pistons will produce different amounts of noise. The following table illustrates a first range of net index angles and a second range of net index angles that will produce lower noise related to flow pulsations than the noise produced at a net index angle of zero or half the separation angle for pumps ranging from five to thirty-five pistons in each rotating group. In the following tables, the N represents the number of pistons in each rotating group:

Net index angle (in Deg) First Range Second Range N Minimum Maximum Minimum Maximum 5 8.64 27.36 44.64 63.36 7 6.17 19.54 31.89 45.26 9 4.80 15.20 24.80 35.20 11 3.93 12.44 20.29 28.80 13 3.32 10.52 17.17 24.37 15 2.88 9.12 14.88 21.12 17 2.54 8.05 13.13 18.64 19 2.27 7.20 11.75 16.67 21 2.06 6.51 10.63 15.09 23 1.88 5.95 9.70 13.77 25 1.73 5.47 8.93 12.67 27 1.60 5.07 8.27 11.73 29 1.49 4.72 7.70 10.92 31 1.39 4.41 7.20 10.22 33 1.31 4.15 6.76 9.60 35 1.23 3.91 6.38 9.05

In an exemplary embodiment, a pump 10 having eleven pistons 23 in each rotating group 20 and 50 may have a low noise net index angle set at any angle from 3.93 degrees to 12.44 degrees and from 20.29 degrees to 28.80 degrees. If the net index angle 93 is set within either of these two ranges, the noise produced by the floating cup pump 10 will be less than the noise produced by the same pump 10 when the net index angle is zero or half the separation angle.

In addition to the low noise net index angles ranges, each pump also has a low best low noise net index angle and a high best low noise net index angle. The following table illustrates the angles producing the least amount of noise related to flow pulsations for pistons having five to thirty-five pistons in each rotating group:

Best Net Index Angle (in degrees) N Low Best High Best 5 18 54 7 13 39 9 10 30 11 8.2 25 13 6.9 21 15 6.0 18 17 5.3 16 19 4.7 14 21 4.3 13 23 3.9 12 25 3.6 11 27 3.3 10 29 3.1 9.3 31 2.9 8.7 33 2.7 8.2 35 2.6 7.7

In an exemplary embodiment, a pump 10 having eleven pistons 23 in each rotating group 20 and 50 may have two best low noise net index angles where the noise related to flow pulsations produced by the floating cup pump 10 will be less than the noise produced by the same pump 10 at any other net index angle including the zero index angle and half the separation angle. In a twenty-two piston floating cup pump, the two best angles are about 8.2 degrees and about 25 degrees. The term about means that when a number is rounded to a like number of significant digits, the numbers are equal. Thus both 8.15 and 8.24 are equal to 8.2 and 24.5 and 25.4 are equal to 25.

The two tables explained above serve to teach those skilled in the art that the obvious choices of zero or half the separation angle as the net index angle are not the best angles when trying to reduce the noise generated from flow pulsations in tandem floating cup pumps having an odd number of pistons. Further, the tables described above provide those skilled in the art with ranges of low noise index angles as well as best net index angles to choose from.

INDUSTRIAL APPLICABILITY

The present disclosure finds potential application in any tandem floating cup pump having an odd number of pistons. The present disclosure aims to solve the recently recognized issue of noise related to flow pulsations in tandem floating cup pumps having an odd number of pistons is different from similar pumps with even number of pistons.

A floating cup pump 10 displaces fluid by rotating a shaft 18 that may rotate the rotor 12 and the rotating groups 20 and 50. Because the pistons 23 are attached to the rotor 12, the pistons 23 may rotate along with the shaft 18 and the rotor 12. Consequently, the entire first and second rotating groups 20 and 50 rotate along with the first and second barrel plates 26 and 56 also rotate with the shaft 18 at the same speed. Pistons 23 of the first rotating group 20 and the second rotating group 50 perform similar functions as they rotate about the shaft 18. In one cycle of operation, each piston 23 rotates a full circle around the shaft 18, arriving at the same position that the piston 23 started at. At the end of the full circle, each piston 23 displaces a fixed amount of fluid that is equal in all pistons 23. The manner in which a piston 23 displaces fluid may be explained by discussing an exemplary piston's rotational path in FIG. 4. Assume a piston 123 from the first rotating group 120 is an exemplary piston. The piston 123 received by a corresponding floating cup 131, is at the bottom dead center of the first rotating group 20. In this particular embodiment, the floating cup 131 has maximum fluid volume with the piston 123 at its greatest distance from the bottom end 134 of the floating cup 131. Further, the first port plate is aligned such that the floating cup is positioned at the bottom-blocked portion of the port plate. Here, no fluid is being displaced because the floating cup is at neither the inlet port 148 nor outlet port 149 of the first port plate. The rotating group, including the piston and the floating cup then begins to rotate around the first port plate. As the rotating group 120 rotates further, the floating cup 131 begins to displace fluid into the outlet port 149. The piston 123 moves closer to the bottom end 134 of the floating cup 131 while the fluid volume inside the floating cup 131 drops by letting fluid into the outlet port 149 of the first port plate. The rotating group 120 then reaches the top dead center of the rotating group 120 where the piston 123 is now at its closest distance from the bottom end 134 of the floating cup 131 and where the fluid volume inside the floating cup 131 is at its least volume. The bottom end 134 of the floating cup 131 is oriented with the top blocked portion of the port plate 140 and therefore, no fluid displacement is taking place. As the rotating group 120 continues rotating along the circle, the piston 123 begins to move away from the bottom end 134 of the floating cup 131. The bottom end 134 of the floating cup 131 moves into the inlet port 148 and begins to fill up the volume of the floating cup 131 as it rotates towards the bottom dead center. Once the piston returns to the bottom dead center and completes one cycle of rotation, the piston is again at its farthest distance from the bottom end of the floating cup. The floating cup has maximum fluid volume and is aligned with the bottom-blocked portion of the port plate again. In the floating cup pump in FIG. 4, the pump 110 has a zero net index angle. Here, the orientation of the bottom dead centers of both rotating groups 120 and 150, respectively coincide with the exact same point on both the port plates.

In the floating cup pump 210 shown in FIG. 5, the pump 210 has a net index angle that is not zero or half the separation angle. The piston index angle is zero as both pistons 223 are aligned with one another. The port plate index angle 292 however, is non-zero and equal to the net index angle. When the two rotating groups 220 and 250 are offset by the net index angle, the bottom dead centers and top dead centers of the first rotating group 220 and the second rotating group 250 align with a specific point on their respective port plates at different times. During one cycle of rotation, the floating cup 231 from the first rotating group 220 displaces fluid in the outlet port 249 of the first port plate while the floating cup 231 from the second rotating group 250 is still oriented with the inlet port 274 of the second port plate. Although both rotating groups 220 and 250 displace an equivalent volume of fluid, the first rotating group 220 displaces fluid out to the outlet port a little earlier than the second rotating group 250. By offsetting the port plates, the time during which both rotating groups 220 and 250 are not displacing any fluid may be reduced.

This disclosure describes a floating cup pump that reduces the noise related to flow pulsations produced by a pump relative to the noise related to flow pulsations produced by a pump that has a zero net index angle or a net index angle of half the separation angle. Further, the disclosure discusses two alternate ways of setting the net index angle including setting a piston index angle via a rotor or setting a port plate index angle by offsetting the port plates relative to each other. The disclosure teaches those skilled in the art the best net index angles that will produce the least noise related to flow pulsations in a tandem floating cup pump having an odd number of pistons. The disclosure also provides the associated ranges of net index angles that produce less noise related to flow pulsations than a pump having a zero net index angle or a net index angle of half the separation angle.

It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims. 

1. A method for reducing flow pulsations in a tandem floating cup pump having an odd number of pistons in each of a first and second rotating group, each piston on each rotating group spaced equally apart from an adjacent piston by a separation angle, comprising the steps of: determining a low noise net index angle that corresponds to reduced flow pulsations with respect to the flow pulsations produced at a net index angle of zero and the flow pulsations produced at a net index angle of half the separation angle; setting a net index angle between a top dead center orientation of the first rotating group relative to a top dead center orientation of the second rotating group to the low noise net index angle.
 2. The method of reducing flow pulsations of claim 1 wherein the step of setting the net index angle to the low noise net index angle is performed by offsetting a first port plate relative to a second port plate by the low noise net index angle.
 3. The method of reducing flow pulsations of claim 1 wherein the step of setting the net index angle to the low noise net index angle is performed by offsetting the first rotating group relative to the second rotating group by the low noise net index angle via a rotor.
 4. The method of reducing flow pulsations of claim 1 wherein the determining step includes the steps of: selecting the number of pistons on each rotating group; determining a net index angle by choosing an angle greater than one of a minimum angle of a first range and a minimum angle of a second range, but less than one of a maximum angle of a first range and a maximum angle of a second range, respectively, that corresponds to the selected number of pistons in each rotating group, using the following table: Net index angle (in Deg) First Range Second Range N Minimum Maximum Minimum Maximum 5 8.64 27.36 44.64 63.36 7 6.17 19.54 31.89 45.26 9 4.80 15.20 24.80 35.20 11 3.93 12.44 20.29 28.80 13 3.32 10.52 17.17 24.37 15 2.88 9.12 14.88 21.12 17 2.54 8.05 13.13 18.64 19 2.27 7.20 11.75 16.67 21 2.06 6.51 10.63 15.09 23 1.88 5.95 9.70 13.77 25 1.73 5.47 8.93 12.67 27 1.60 5.07 8.27 11.73 29 1.49 4.72 7.70 10.92 31 1.39 4.41 7.20 10.22 33 1.31 4.15 6.76 9.60 35 1.23 3.91 6.38 9.05

wherein N represents the number of pistons in each rotating group.
 5. The method of reducing flow pulsations of claim 4 wherein the determining step includes the steps of: selecting the number of pistons on each rotating group; determining a net index angle by choosing an angle about equal to one of a low best angle and a high best angle, that corresponds to the selected number of pistons in each rotating group, using the following table: Best Net Index Angle (in degrees) N Low Best High Best 5 18 54 7 13 39 9 10 30 11 8.2 25 13 6.9 21 15 6.0 18 17 5.3 16 19 4.7 14 21 4.3 13 23 3.9 12 25 3.6 11 27 3.3 10 29 3.1 9.3 31 2.9 8.7 33 2.7 8.2 35 2.6 7.7

wherein N represents the number of pistons in each rotating group.
 6. A floating cup pump, comprising: a rotor, a first barrel plate and a second barrel plate, attached to a shaft; a first rotating group comprising a first set of an odd number of floating cups, each floating cup swivelly attached to the first barrel plate, a first set of an odd number of pistons, each piston being equally spaced apart from an adjacent piston by a separation angle and each piston having a first end and a second end, the first end of each piston attached to the rotor, the second end of each piston received by a respective one of the first set of floating cups; a second rotating group comprising a second set of the odd number of floating cups, each floating cup swivelly attached to the second barrel plate, a second set of pistons, having a same number of pistons as the first rotating group, each piston being equally spaced apart from an adjacent piston by the separation angle and each piston having a first end and a second end, the first end of each piston attached to the rotor, the second end of each piston received in a respective one of the second set of floating cups; the first rotating group and the second rotating group having a first relative orientation, the first relative orientation defining a piston index angle; a first port plate adjacent the first barrel plate defining a bottom dead center position of the first rotating group; a second port plate adjacent the second barrel plate defining a bottom dead center position of the second rotating group; the bottom dead center of the first rotating group and the bottom dead center of the second rotating group having a second relative orientation, the second relative orientation defining a port plate index angle; a low noise net index angle being the sum of the piston index angle and the port plate index angle, wherein the low noise net index angle is different from zero and half of the separation angle.
 7. The floating cup pump of claim 6 wherein the low noise net index angle depends on the number of pistons in each rotating group.
 8. The floating cup pump of claim 6 wherein the port plate index angle is the low noise net index angle, and the piston index angle is zero.
 9. The floating cup pump of claim 6 wherein the piston index angle is the low noise net index angle, and the port plate index angle is zero.
 10. The floating cup pump of claim 6 wherein each rotating group has eleven pistons and the low noise net index angle is about equal to one of 8 degrees and 25 degrees.
 11. The floating cup pump of claim 6 wherein the low noise net index angle for an odd number of pistons ranging from 5 to 35 pistons in each rotating group is one of the greater than the minimum of the first range and less than the maximum of the first range, and greater than the minimum of the second range and less than the maximum of the second range, respectively, with respect to the following table: Net index angle (in Deg) First Range Second Range N Minimum Maximum Minimum Maximum 5 8.64 27.36 44.64 63.36 7 6.17 19.54 31.89 45.26 9 4.80 15.20 24.80 35.20 11 3.93 12.44 20.29 28.80 13 3.32 10.52 17.17 24.37 15 2.88 9.12 14.88 21.12 17 2.54 8.05 13.13 18.64 19 2.27 7.20 11.75 16.67 21 2.06 6.51 10.63 15.09 23 1.88 5.95 9.70 13.77 25 1.73 5.47 8.93 12.67 27 1.60 5.07 8.27 11.73 29 1.49 4.72 7.70 10.92 31 1.39 4.41 7.20 10.22 33 1.31 4.15 6.76 9.60 35 1.23 3.91 6.38 9.05

wherein N represents the number of pistons in each rotating group.
 12. The floating cup pump of claim 6 wherein the low noise net index angle for an odd number of pistons ranging from 5 to 35 pistons in each rotating group is about equal to one of a low best and a high best, with respect to the following table: Best Net Index Angle (in degrees) N Low Best High Best 5 18 54 7 13 39 9 10 30 11 8.2 25 13 6.9 21 15 6.0 18 17 5.3 16 19 4.7 14 21 4.3 13 23 3.9 12 25 3.6 11 27 3.3 10 29 3.1 9.3 31 2.9 8.7 33 2.7 8.2 35 2.6 7.7

wherein N represents the number of pistons in each rotating group.
 13. A floating cup pump, comprising: a rotor, a first barrel plate and a second barrel plate, attached to a shaft; a first rotating group comprising a first set of an odd number of floating cups, each floating cup swivelly attached to the first barrel plate, a first set of an odd number of pistons, each piston being equally spaced apart from an adjacent piston by a separation angle and each piston having a first end and a second end, the first end of each piston attached to the rotor, the second end of each piston received by a respective one of the first set of floating cups; a second rotating group comprising a second set of the odd number of floating cups, each floating cup swivelly attached to the second barrel plate, a second set of pistons, having a same number of pistons as the first rotating group, each piston being equally spaced apart from an adjacent piston by the separation angle and each piston having a first end and a second end, the first end of each piston attached to the rotor, the second end of each piston received in a respective one of the second set of floating cups; the first rotating group and the second rotating group having a first relative orientation, the first relative orientation defining a piston index angle; a first port plate adjacent the first barrel plate defining a bottom dead center position of the first rotating group; a second port plate adjacent the second barrel plate defining a bottom dead center position of the second rotating group; the bottom dead center of the first rotating group and the bottom dead center of the second rotating group having a second relative orientation, the second relative orientation defining a port plate index angle; a net index angle being the sum of the piston index angle and the port plate index angle; and means, including setting the net index angle to a low noise net index angle different from zero and half the separation angle, for reducing noise due to flow pulsations.
 14. The floating cup pump of claim 13 wherein the means for reducing noise due to flow pulsations reduces the noise to lower than the noise produced when the net index angle is zero.
 15. The floating cup pump of claim 13 wherein the means for reducing noise due to flow pulsations reduces the noise to lower than the noise produced when the net index angle is half the separation angle.
 16. The floating cup pump of claim 13 wherein the port plate index angle is the low noise net index angle, and the piston index angle is zero.
 17. The floating cup pump of claim 13 wherein the piston index angle is the low noise net index angle, and the port plate index angle is zero.
 18. The floating cup pump of claim 13 wherein each rotating group has eleven pistons and the net index angle is about equal to one of 8 degrees and 25 degrees.
 19. The floating cup pump of claim 13 wherein the low noise net index angle for an odd number of pistons ranging from 5 to 35 pistons in each rotating group is one of the greater than the minimum of the first range and less than the maximum of the first range, and greater than the minimum of the second range and less than the maximum of the second range, respectively, with respect to the following table: Net index angle (in Deg) First Range Second Range N Minimum Maximum Minimum Maximum 5 8.64 27.36 44.64 63.36 7 6.17 19.54 31.89 45.26 9 4.80 15.20 24.80 35.20 11 3.93 12.44 20.29 28.80 13 3.32 10.52 17.17 24.37 15 2.88 9.12 14.88 21.12 17 2.54 8.05 13.13 18.64 19 2.27 7.20 11.75 16.67 21 2.06 6.51 10.63 15.09 23 1.88 5.95 9.70 13.77 25 1.73 5.47 8.93 12.67 27 1.60 5.07 8.27 11.73 29 1.49 4.72 7.70 10.92 31 1.39 4.41 7.20 10.22 33 1.31 4.15 6.76 9.60 35 1.23 3.91 6.38 9.05

wherein N represents the number of pistons in each rotating group.
 20. The floating cup pump of claim 13 wherein the low noise net index angle for an odd number of pistons ranging from 5 to 35 pistons in each rotating group is about equal to one of a low best and a high best, with respect to the following table: Best Net Index Angle (in degrees) N Low Best High Best 5 18 54 7 13 39 9 10 30 11 8.2 25 13 6.9 21 15 6.0 18 17 5.3 16 19 4.7 14 21 4.3 13 23 3.9 12 25 3.6 11 27 3.3 10 29 3.1 9.3 31 2.9 8.7 33 2.7 8.2 35 2.6 7.7

wherein N represents the number of pistons in each rotating group. 